In this dissertation, the drop interactions with a single fiber is discussed under an application angle for the development on new Drop-on-Demand (DOD) printhead using a fiber-in-a-tube platform[1] to print highly viscous materials[2]. To control the drop formation and manipulation on fiber, one needs to know how the fiber wetting properties and the fiber diameter influence drop formation. And then, one needs to know the effects of fiber movement in the device on drop formation. These two questions constitute the main theme of this dissertation.
Before this study, it was accepted that the liquids could not form axisymmetric droplets if the liquid drop makes the contact angle greater than 90 degrees on a flat substrate of the same material. In Chapter 2, all possible configurations of an axisymmetric drop wrapping up the fiber were analyzed rigorously by studying all solutions of the Laplace equation of capillarity for small droplets for which gravity is insignificant. In Chapter 3, an experimental analysis of morphological transitions of droplet configurations has been systematically conducted. When the droplets are large and are able to wrap up the fiber, they form barreled configurations; when the volume of droplets is small, the barrels cannot be formed and droplets rest as clamshells on the fiber side. With these analyses in hands, one can design of a fiber-in-a-tube printhead taking advantage of the established diagrams for formation of barreled droplets.
Drop-on-demand (DOD) printing is a versatile manufacturing tool, which has been widely used in applications ranging from graphic products to manufacturing of ceramics, even for cell engineering. However, the existing DOD methods cannot be applied for highly viscous materials: the printing technologies are typically limited to the inks with the water level viscosity and fall short of ejecting jets from thick fluids and breaking them into droplets. To address this challenge, a new wire-in-a-tube technology for drop generation has been developed replacing the nozzle generator with a wire-in-a-tube drop generator. In Chapter 4, we introduce the wire-in-a-tube generator and show successful printing results of droplets on-demand from highly viscous (~10 Pa*s) liquids. In Chapter 5, we study the drop formation mechanisms in the wire-in-a-tube drop generators. These mechanisms couple unique fluid mechanics, capillarity, and wetting phenomena providing a new platform that can be used in different microfluidic applications
